Federal air marshals have begun following ordinary US citizens not suspected of a crime or on any terrorist watch list and collecting extensive information about their movements and behavior under a new domestic surveillance program that is drawing criticism from within the agency.

The previously undisclosed program, called “Quiet Skies,” specifically targets travelers who “are not under investigation by any agency and are not in the Terrorist Screening Data Base,” according to a Transportation Security Administration bulletin in March.

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Already under Quiet Skies, thousands of unsuspecting Americans have been subjected to targeted airport and inflight surveillance, carried out by small teams of armed, undercover air marshals, government documents show. The teams document whether passengers fidget, use a computer, have a “jump” in their Adam’s apple or a “cold penetrating stare,” among other behaviors, according to the records.

TSA officials, in a written statement to the Globe, broadly defended the agency’s efforts to deter potential acts of terror. But the agency declined to discuss whether Quiet Skies has intercepted any threats, or even to confirm that the program exists. Release of such information “would make passengers less safe,” spokesman James Gregory said in the statement.

Already under Quiet Skies, thousands of unsuspecting Americans have been subjected to targeted airport and inflight surveillance, carried out by small teams of armed, undercover air marshals, government documents show. The teams document whether passengers fidget, use a computer, have a “jump” in their Adam’s apple or a “cold penetrating stare,” among other behaviors, according to the records.

Air marshals note these observations — minute-by-minute — in two separate reports and send this information back to the TSA.

Did you scan the boarding area from afar?

Have a cold, penetrating stare?

Sleep on the plane? Use the bathroom? Talk to others?